Luminescent image device and combinations thereof with optical filters



July 8, 1969; s. LARACH ETAL LUMINESCENT IMAGE DEVICE AND COMBINATIONSTHEREOF WITH OPTICAL FILTERS Filed Jan. 16. 1964 I I I n h 0/ v. f

WA VELEAM 7 4- III/61770015 United States Patent (3 U.S. Cl. 178-7.86 9Claims ABSTRACT OF THE DISCLOSURE A cathode ray tube using high emissionintensity, narrow band emitting phosphor and having spectacle or filtermeans matched to the narrow bands of the phosphors.

This invention relates to luminescent image devices such as cathode raytubes and to combinations of luminescent image devices and opticalfilter means.

As used herein: (a) the peak emission of a phosphor is that maximumlight output which, under excitation, occurs at some specific spectralwavelength as compared to the lesser light output which occurs atimmediately shorter and longer spectral wavelengths; (b) the peakemission intensity of a phosphor is the amount of light output in anextremely narrow band of wavelengths centered at the wavelengths of thepeak emission which is produced by a given intensity of excitation; thetotal emission intensity of a phosphor is the amount of light output atall wavelengths of the phosphors emission which is produced by a givenintensity of excitation. When the emission intensities of two phosphorsare compared with each other, the phosphors are considered to besubjected to equal excitation, and in the same manner at an intensitylevel within the range of normal, practical operating conditions; (c)the emission band of a phosphor is the spectral range of wavelengthswithin which the luminescent emission is concentrated, the width of theband being equal to the spectral range at one-half the peak emission;(d) the transmission band of a filter is the spec tral range ofwavelengths within which the transmission of the filter is concentrated,the width of the band being equal to the spectral transmission range atone-half the peak transmission; (6) the matching of a filtertransmission band with a phosphor emission band means that the filtertransmission band and the phosphor emission band are centered atapproximately the same spectral wavelength. The filter transmission bandwidth may be narrower than, substantially equal to, or slightly widerthan the width of the phosphor emission band; (f) when one phosphoremission band is described as falling within or outside of anotherphosphor emission band, it is meant that that portion of the spectralband which defines the one phosphors band width is within or outsidethat portion of the other spectral band which defines the otherphosphors width; (g) the term standard Pl phosphor means themanganese-activated zinc orthosilicate phosphor identified as No. 1021and standardized by the U.S. National Bureau of Standards; and (h) theterm unaided eye means without the use of an optical filter but does notexclude the use of optical corrective lenses as may be required for aparticular observer.

ice

face of the device and ambient light reflected from the face of thedevice.

Another object of this invention is the provision of a novel arrangementof luminescent image device and optical filter means which enables aviewer to selectively discriminate between ditferent imagessimultaneously displayed on the phosphor screen of the device.

In accordance with the invention, the phosphor screen of a luminescentimage device includes a phosphor having a very high peak emissionintensity (e.g., six times that of the standard Pl phosphor) andpreferably a narrow (e.g., less than one hundred angstroms) emissionband. Images displayed on the screen are observed through an opticalfilter (e.g., an interference type) which has a narrow transmission bandof, e.g., less than angstroms and which is approximately matched to theemission band of the phosphor. The filter is located remote from thephosphor screen between the ambient light and the observer, e.g., as apair of spectacles worn by the observer.

For the purpose of brevity and clarity, the invention is hereinafterdescribed by way of example as involving a cathode ray tube having acathodoluminescent phosphor screen. However, other luminescent imagedevices may instead be used in the practice of the invention, e.g.,panel display devics having electroluminescent phosphor screens, anddisplay means having X-ray and ultra-violet excited phosphor screens.

It has long been known that an absorption type optical filter can bespectrally matched with, and disposed adjacent to, the phosphor screenof a cathode ray tube to improve the image quality when the tube isviewed under high ambient light conditions. Examples of such knowledgeappear in U.S. Patent 2,419,177 issued to Albert Steadman on Apr. 15,1947, and in U.S. Patent 3,013,114 issued to J. E. Bridges on Dec. 12,1961.

The prior art taught that even in combination with a suitable filter, inorder to get a high ratio of image brilliance to background brilliance,the phosphor of a cathode ray tube screen had to have a broad emissionband so as to produce an image of high brilliance. Thus, to substitute anarrow band phosphor for the prior art broad band phosphor, even thoughthe narrow band phosphor might have a high peak emission intensity,would be contrary to the teaching of the prior art because decrease oftotal light output was believed to be unacceptable. This belief may havebeen prompted, at least in part, by the fact that even where a broadband absorption type faceplate filter was optimumly matched with theconventional broadband luminescent emission of a cathode ray tube, theimprovement in image contrast was marginal. Such mar ginal improvementresulted because the filter, being broad handed to match the phosphor,failed to attenuate a sufficiently large percentage of the ambient lightwhich fell upon the phosphor screen. Similarly, to substitute a narrowband interference filter for the prior art broad band absorption filterwould produce no advantage since this would decrease the observablelight of the luminescent image as well as the unwanted ambient light.Furthermore, since narrow band interference filters reflect rather thanabsorb the non-transmitted light, the use of an interference filter as aprior art substitution would increase the reflection of ambient lightfrom the faceplate-filter combination and thus even further degrade theimage contrast.

The degree of improvement provided by the present invention over theprior art can be seen by comparing the effectiveness of ambient lightelimination by the present arrangement with that by a typical prior artarrangement in which a broad band absorption filter is matched with abroad band phosphor and positioned adjacent to the phosphor screen.Because the filter in the prior art arrangement is positioned adjacentto the phosphor screen, none of the ambient light directed to theobserver is eliminated. On the other hand, because the filter of thepresent arrangement is positioned at the observer, it eliminatessubstantially all of such light, only that small portion of such lighthaving wavelengths which lie within the narrow transmission band of thefilter not being greatly attenuated.

The ambient light which would, in the absence of any filter, fall on theface of the image device and be reflected to the obesrver may be dividedinto two classes, viz., that having wavelengths which lie within thetransmission band of the filter and that having Wavelengths which falloutside the transmission band of the filter. The first of these twoclasses of light is not significantly attenuated by either the prior artarrangement or the present arrangement. However, since the filter of thepresent arrangement has a transmission band, e.g., one-fifth as wide asthe filter of the prior art arrangement (e.g., 100 angstroms as opposedto 500 angstroms), there is only one-fifth as much of this unattenuatedlight which reaches the observer in the present arrangement. Of thesecond of these two classes of light, substantially all thereof iseliminated by the filter of the present arrangement. On the other hand,because the filter of the prior art arrangement is positioned adjacentto the phosphor screen, a significant portion, of this light isreflected from the front face of the filter toward the observer. Suchlight is the most detrimental of all to image contrast since itincreases the apparent luminous level of the image background.Therefore, the present arrangement eliminates many times the ambientlight that the prior art arrangement eliminates and provides a contrastratio which is many times that provided by the prior art arrangement.

In the drawings:

FIG. 1 is a graph illustrating the spectral energy emissioncharacteristics of a high-peak, narrow-band phosphor suitable for use inthis invention and comparing it with the spectral energy emissioncharacteristics of conventional broad-band phosphors; and

FIGS. 2, 3, and 4 are schematic views of different embodiments of theinvention.

Phosphors suitable for use in the practice of this invention preferablyhave a relatively high peak emission intensity. Theoretically, theabsolute value of the peak emission necessary to provide a satisfactoryimage presentation depends upon the brilliance of the ambient orbackground light. If the ambient or background light is of lowbrilliance, then the peak emission intensity of the phosphor can becorrespondingly low and still produce a satisfactory image. Even inbright sunlight ambient, a favorable positioning of the display screenfacing away from direct radiation of the sun lessens the phosphor peakemission intensity requirements. In order to provlde satisfactoryoperation in high ambient light, e.g., in bright sunlight, it ispreferred that peak emission intensity of the phosphor be greater thanthe solar radiant power density at the spectral wavelength of thephosphors peak emission. (See, e.g., FIG. 25-1 of IES Lighting Handbook,Illuminating Engineering Society, New York, N.Y.) Under the most adverseambient light conditions where gray-scale image production is desired,the phosphor peak emission intensity is preferably at least tw ce thesolar radiant power density, or, as compared with standard phosphors,about six or more times the peak emission intensity of the standard P1phosphor. Also theoretically, the emission band of the phosphor need notbe limited to some maximum allowable width. If the emission band isgreater than the width of the transmission band of the filter used incombination with the phosphor, the filter will block out thephosphorluminescence which does not fall within the transmission band ofthe filter. Some of the emitted energy is then wasted. However, in orderthat a phosphor exhibit the desired peak emission intensity, itordinarily must also have a relatively narrow emission band into whichthe total luminescent energy is concentrated, usually less than about100 angstroms. This situation exists because of a theoretical limit ofmaximum energy conversion efficiency of phosphors in general and becauseof the factors which dictate the practical limits of the amount ofenergy which can be applied to excite the phosphor.

Phosphors having the desired characteristics as set forth abovegenerally contain rare-earth activators, viz, those elements of thePeriodic Table numbered 58 (cerium) through 71 (lutetium). The preferredphosphors are those having a host crystal of a zinc and/ or cadmiumchalcogenide. Such preferred phosphors are hereinafter described indetail in the appendix which follows.

In FIG. 1, the curve 10 depicts the response characterv istic of acathodoluminescent, thulium-activated zinc sulfide phosphor (ZnSaTm),which at 20 C. has an emission band width of approximately 75 angstromsand which peaks at approximately 4.773 angstroms. This phosphor isdescribed in detail as Example 5 in the appendix. Considering thevisible spectrum to be about 3,800 angstroms wide (3,8007,600angstroms), this narrow band phosphor has an emission band width whichis less than one-fiftieth of the visible spectrum.

The curve 10 of the ZnSzTm phosphor, is shown superimposed on theresponse characteristic curve 14 of a conventional P4 sulfide phosphorscreen comprising silver activated zinc sulfide and silver activatedzinc-cadmium sulfide such as that described in the booklet RCA Phosphorspublished by Radio Corporation of America in 1961. Such asuperimposition illustrates that the rareearth activated phosphor has apeak emission which is approximately six times the peak emission of theP4 phos phor. On the other hand, because of the very narrow band widthof the rare-earth activated phosphor, its total luminescence issubstantially less than the total luminescence of the P4 phosphor.Nevertheless, when used in one of the arrangements hereinafterdescribed, this phosphor produces high contrast images in brightsunlight.

Optical filters suitable for use in the practice of the invention shouldhave a relatively narrow transmission band, e.g., less than one-fortiethas Wide as the visible spectrum. Interference type filters areespecially desirable because these have narrow band transmissioncharacteristics. Typical filters of the interference type, having atransmission band of angstroms or less, are commercially available fromseveral filter manufacturers. The characteristics of such filters aredescribed, for example, in Principles of Optics, by Max Barn and EmilWolf, Pergamon Press Inc., New York, N.Y., 1959'.

Cathode ray tubes having different forms of screens which includehigh-peak narrow-band emission phosphors and combinations thereof withdifferent forms of narrowband optical-filter means are described in thefollowing examples.

EXAMPLE A FIG. 2 illustrates a luminescent image device, e.g., a cathoderay tube 22, which includes a phosphor screen 24. To present amonochrome image, the phosphor material of the screen 24 may, forexample, com-prise blueemitting ZnSzTm as described in Example 5 of theappendix and whose response characteristic curve 10 is illustrated inFIG. 1. An observer 26 is provided with a pair of spectacles 28. Thelenses 30 and 32 of the spectacles 28 comprise narrow band opticalfilters. Each of the filter lenses 30 and 32 has a narrow, e.g., 100angstrom wide, transmission band which is centered at the wavelength ofthe peak emission of the phosphor screen 24. An ambient light source 34,such as the sun or an incandescent light bulb, illuminates the spacesurrounding the image device 22. The filter lenses 30 and 32, beingpositioned between the observer 26 and the ambient light, serve to blockfrom the observer 26 all of the ambient light except that which fallswithin the very narrow transmission band of the filter lenses 30 and 32.This includes not only that light which is reflected from the face ofthe image device 22, but also that light which is directed from thesource 34 toward the observers eye. As a result of such elimination, theobserver 26 views a readily discernible, high-contrast image on thescreen 24, notwithstanding the lower brilliance of the image due to thenarrow emission band properties of the phosphor screen 24.

Where use in bright sunlight is anticipated, the spectacles 28 may, ifdesired, be such that the narrow band optical filter means matched tothe phosphor emission band is provided as only a part of each lens 30,32, e.g., in a manner similar to a bifocal lens. The remainder of eachlens is provided as a more conventional neutral grey or green absorptiontype filter sun glass lens.

EXAMPLE B FIG. 3 illustrates another luminescent image device, e.g., acathode ray tube 36, which includes a phosphor screen 38. To present amonochrome image, the phosphor of the screen 38 may, for example,comprise the blue-emitting ZnSzTm of Example A. An observer 39 islocated in an enclosure 40 having a window 42 therein through which hemay observe the phosphor screen 38. The window 42 comprises a narrowband optical filter having a transmission band of, e.g., 100 angstromswhich is centered at the wavelength of the peak emission of the phosphorscreen 38. Since the observer 39 is separated from the ambient lightsource 34 by the enclosure 40, all of the ambient light except thatlight which falls within the transmission band of the filter window 42is blocked from the observer 39.

EXAMPLE C In accordance with another arrangement the phosphor screen 24(FIG. 2) includes a blue-emitting, narrow band phosphor and ayellow-emitting, broad band phosphor. The blue-emitting phosphor may beZnS:TmLi (Example 7 of the appendix) having an emission band ofapproximately 70 angstroms. The yellow-emitting phosphor may be a(Zn:Cd)S:Ag material having a zinc sulfide to cadmium sulfide ratio ofabout 45/55 and a silver content of about 0.005 weight percent andhaving an emission band width of about 1300 angstroms. The emission bandof the narrow band ZnSzTmLi phosphor lies outside of, and is spacedfrom, the emission band of the broad band (Zn:Cd)S:Ag phosphor. Theblue-emitting ZnS :TmLi and the yellow-emitting (Zn:Cd)S:Ag are mixed ina weight ratio of 3/ 1.

Under relatively low ambient light conditions the observer 26 views thescreen without the use of the filter and sees a black and white image.Under relatively high ambient light conditions, the observer 26 wearsthe spectacles 28, whose lenses have a narrow, e.g., not substantiallygreater than 100 angstroms, transmission band matched to the emissionband of the ZnSzTmLi prosphor and sees a blue monochrome image ofgreatly improved visibility and contrast over that observable withoutthe spectacles 28.

As a variation to this example, a similar arrangement may be used withthe FIG. 3 apparatus wherein the filter window 42 is provided with theproper narrow transmission band.

EXAMPLE D In the arrangement of FIG. 2, the tube 22 may comprise a colorcathode ray tube, such as one having a phosphor screen 24 composed ofthree different color emitting phosphors which are adapted to beselectively excited to produce a color image. The tube 22 may, forexample, comprise: a mosaic dot screen shadow mask type tube such as thecommercially available RCA ZIFBPZZ; a mosaic line-screen feedback tubesuch as that described in US. Patent 2,932,756, issued to ArthurLiebscher on Apr. 12, 1960; or a three layer screen penetration typetube such as that described in US. Patent 2,455,710 issued to C. S.Szegho on Dec. 7, 1948. The three phosphors of the color screen 24 maycomprise the narrow band blueemitting ZnSzTm phosphor (Example 5 of theappendix) and conventional or modified broad-band red-emitting andgreen-emitting silver activated zinc-cadmium sulfide phosphors (e.g.,P22 phosphors in RCA Phosphors booklet supra). Each of the filter lenses30 and 32 worn by the observer 26 are made to have a single narrowtransmission band matched to the emission band of the blue-emittingZnS:Tm phosphor. Under high ambient light conditions the observer 26views a blue monochrome image through the filter lenses; under lowambient light conditions the observer 26 removes the filter lenses andviews a fullcolor image.

In a variation of this example, the filter means may be provided asillustrated in FIG. 3. The filter window 42 is made to have a singlenarrow transmission band matched to the blue-emitting ZnSzTm phosphor.

EXAMPLE E In certain applications of cathode ray tubes, a plurality ofdifferent images are simultaneously displayed on a single screen and acorresponding pluraity of observers view the screen to visually select asingle image. Such applications, for example, may involve a trafiiccontrol system wherein three different kinds of information, forexample: (a) aircraft on the runways of an airport; (b) aircraft in aholding pattern aloft adjacent to the airport; and (c) aircraftapproaching the airport from afar, are imaged on a single phosphorscreen. Each of three different men is assigned the job of observing andprocessing a different one of these images. However, because of thesuperimposition of the images-notwithstanding the fact that they are indifferent colors, e.g., green, yellow, and b1uediscrimination by oneobserver of the information for which he is responsible is oftenconfusing and difiicult.

FIG. 4 illustrates an arrangement wherein a plurality of images on asingle screen may be observed by a plurality of observers, each of whomsees only that information for which he is responsible. In FIG. 4, animage display device, e.g., a cathode ray tube 44 includes a phosphorscreen 46 which is composed of three different narrow-band emissionphosphors, each of which can be separately excited with a differentinformation presenta tion. For example, the tube 44 may comprise eithera shadow mask tube or a line screen feedback type tube as hereinbeforereferred to. The three phosphors of the screen 46, may, for example,comprise green-emitting erbium-activated zinc sulfide (ZnS:Er)yellow-emitting dysprosium-activated zinc sulfide (ZnS:Dy) and blueemitting thulium-activated Zinc sulfide (ZnSzTm) which are described,respectively, in Examples 1, 2, and 5 of the appendix.

A first observer 48 is provided with a pair of spectacles 50 havingoptical filter lenses each of which is made to have a transmission bandmatched to the emission band of the green-emitting ZnSzEr. A secondobserver 52 is provided with a pair of spectacles 54 having opticalfilter lenses each of which is made to have a transmission band matchedto the emission band of the yellow-emitting ZnS:Dy. A third observer 56is provided with a pair of spectacles 58 having optical filter lenseseach of which is made to have a transmission band matched to theemission band of the blue-emitting ZnSzTm. Thus, each of the observers48, 52, and 56 secs only that image which is displayed in a color whichhis filter spectacles are designed to transmit. Discrimination betweenthat image and the images of the other two colors is substantiallycomplete. This arrangement may find its greater use under conditions oflow ambient ligh where the spectacles serve to facilitate discriminationbetween the different color images. If desired, one or more of theobservers may have filter spectacles that permit him to view two of thedifferent colored images, e.g., by having different filters in thelenses 30 and 32.

7 EXAMPLE F In an application wherein a cathode ray tube is to be viewednot only under high ambient light conditions, but also at times underlow ambient light conditions, it may be desirable to retain, the highlight output capability of a broad band phosphor and also obtain thehigh contrast advantages of the high-peak, narrow band phosphors. Toachieve this end, a cathode ray tube may be provided which has aphosphor screen possessing the combined energy response characteristicsof both a broad band phosphor and a narrow band phosphor.

The broad band phosphor has a higher total emission intensity than doesthe narrow band phosphor. The narrow band phosphor, on the other hand,has a higher peak emission intensity than that of the broad bandphosphor, preferably four or more times higher. The emission band of thenarrow band phosphor is also preferably not greater than about one-tenthas wide as, and lies within, the emission band of the broad bandphosphor.

For example, in a monochrome system according to FIG. 2, the phosphorscreen 24 may comprise narrowband blue-emitting ZnS:Tm (Example of theappendix) and broad band blue-emitting ZnS:Ag such as that whichconstitutes one of the components of a conventional P4 phosphor mix(e.g., see RCA Phosphors booklet, supra). The response characteristicsof these two phosphors are respectively illustrated in FIG. 1 by curveand by the left hand portion 60 of curve 14. In such example, the broadband phosphor has an emission band of about 750 angstroms (4,300-5,050angstroms) peaking at about 4,550 angstroms. The narrow band phosphorhas an emission band of about 75 angstroms (4,7354,810 angstroms)peaking at about 4,773 angstroms.

The observer 26 is provided with filter lenses 30 and 32, each of whichhas a narrow transmission band matched to the emission band of thenarrow band phosphor ZnS:Tm. Under conditions of high ambient light, theobserver 26 views the image presented on the phosphor screen 24 throughthe filter lenses 30 and 32; under low ambient light conditions, theviewer 26 may remove the filter lenses 30 and 32 and view the image onthe screen 24 directly. In either case a blue monochrome image ispresented.

The narrow band phosphor should peak at a wavelength within the bandwidth of the broad band phosphor. In order that the color of the viewedimage both with and without use of the filter be substantially the same,it may be preferred that the narrow band phosphor peak at a wavelengthnear the wavelength at which the broad band phosphor peaks.

The relative proportions of the two phosphors, ZnS:Tm and ZnS:Ag, whichare mixed to provide the screen 24 are dependent upon the particularconditions under which the tube is to be used. If high image contrastunder high ambient light conditions is the primary feature desired, thenthe percentage of the narrow band ZnS:Tm phosphor is increased. On theother hand, if considerable use is to be made of the tube under lowambient light conditions without filter spectacles, then a higherpercentage of the broad band ZnS:Ag phosphor is used.

As a variation of this example the filter arrangement of Example B maybe used instead of the spectacles.

EXAMPLE G An arrangement involving a mixture of broad band and narrowband phosphors can also be used to present a black and white image underlow ambient light conditions and a monochrome image under high ambientlight conditions. The phosphor screen 24 (FIG. 2) may be made of amixture of phosphors including narrow band blue-emitting ZnS:Tm (Example5 of appendix) and of, but in slightly different proportion-s such thatwith the addition of the narrow band ZnS:Tm the screen produces asubstantially white light. With such a screen, filter means as disclosedin either Example A or Example B may be used.

Under high ambient light conditions, the observer 26 uses the filterlens spectacles in viewing the screen 24 and sees a blue monochromeimage; under low ambient light conditions he dispenses with the filterlenses and sees a black and white image having the higher brillianceadvantages which the additional light from the broad-band P4 constituentof the phosphor screen provides.

.As in a monchrome type screen, the emission band of the narrow bandphosphor should lie within the emission band of the board band phosphorof corresponding color.

APPENDIX Some suitable narrow band phosphors may be made by a processwhich comprises reacting a zinc, or cadmium, or zinc-cadmiumchalcogenide with 0.001 to 5.0 mol percent of at least one rare earthelement, as a halide thereof in an oxygen-free ambient, and then coolingthe reaction product. By excluding oxygen from the ambient during thereaciton and by introducing the rare earth element as a halide thereof,this process produces phosphors which exhibit substantial luminescenceemission in relatviely narrow spectral bands.

This process applies to phosphors in which the host material is a zinc,or a cadmium, or zinc-cadmium chalcogenide. Chalcogenides, as usedherein, are sulfides, selenides, tellurides, and mixtures thereof. Thepreferred compositions for the host material are those which producesingle phase solid solutions conventiently, although compositions whichproduce more than one phase may also be used. The range in compositionfor the host material may be represented approximately by the molarformula:

aM SzbM SezcM Te where: M M and M are each at least one member of thegroup consisting of zinc and cadmium a=0.0 to 1.0 mol b=0.l to 1.0 mol0:00 to 1.0 mol, and a-+b+c=1.00

The preferred host material is zinc sulfide. The alternative hostmaterials are those in which cadmium is substituted for part or all ofthe zinc, and/ or selenium and/ or tellurium is substituted for part orall of the sulfur in the preferred zinc sulfide host material.

At least one rare earth activator is included in the host material inproportions of 0.001 to 5.0 mol percent of the host material. A singlerare earth element is preferred as the activator. Combinations of two ormore rare earth elements may be used. The rare earth elements areselected from the rare earth group of the Periodic Table.

. The group consists of elements numbered 58 (cerium) broad bandblue-emitting ZnS:Ag and yellow-emitting I to 71 (lutetium). Thepreferred rare earth elements are determined by the application in whichthe phosphor is to be used. Because of the nature of the processesdescribed herein, the rare earth element is usually trivalent when it isincorporated in the host material. This is the desired valency for theactivator.

Auxiliary activators may be included with the rare earth activator. Theparticular auxiliary activator which is selected depends upon the usefor the phosphor. In the case of electroluminescent phosphors, it isdesirable to include 0.01 to 1.0 mol percent of copper, as an oxygenfreecompound thereof, in the host material.

The phosphors of this process are generally prepared in two steps: (1)preparing a batch of the contituents, and then (2) reacting the batch toproduce the phosphor. The first step is designed to provide a uniformand intimate mixture of the constituents of the phosphor. The mixture ofconstituents should be as free of oxygen and oxygen-containing compoundsas possible. The constituents may be introduced in various alternativeways. Sulfur, selenium, tellurium, zinc, and cadmium may be introducedin elemental form or as oxygen-free compounds thereof. It is preferredthat the constituents of the host material be prepared first byintimately mixing, as by ball milling ch-alcogenides of zinc and cadmiumas required, and then calcining the mixture at about 700 to 1400" C. inan oxygen-free atmosphere, preferably hydrogen sulfide. The calcinedhost material mixture may be mixed or ground again and recalcined ifnecesary. The rare earth activators and auxiliary activators, as halidesthereof, are thenv intimately with the prepared batch of host material.The activators may be introduced as any halide: fluoride, chloride,bromide, and iodide. The batch with the activators therein may also becalcined in an oxygen-free atmosphere to remove any volatile matter andto commence the reaction.

If the phosphor is to contain copper, several alternative methods may beused for introducing the copper activator. In one method, the hostmaterial is slurried with a soluble copper halide and then the slurry isthoroughly dried. After drying, the rare earth halide is addedmechanically by any of the above described processes. In a secondmethod, a compound copper-rare earth sulfide is first prepared in thedesired proportion of copper and rare earth. The compound is then mixedwith the host material, and the mixture calcined in the temperaturerange of 800 to 1200 C. in a hydrogen sulfide atmosphe're. The mixtureis then reground.

One or more fluxes may be included in the batch. A suitable flux is amaterial which melts; that is, forms a liquid phase, at temperaturesbelow 800 C. A flux is introduced to lower the reaction temperature, toaccelera'te the reaction, and/or to produce a more uniform product. Thepreferred fluxes are alkali halides, such as sodium chloride, sodiumbromide, potassium iodide, lithium chloride, and rubidium chloride.

The second step is designed to react the host material and activators toform the phosphor without introducing oxygen. To this end, the mixtureof host material and activators is heated in a non-oxidizing oxygen-freeambient at temperatures between 700 and 1400 C. for 0.1 to hours. In thepreferred process, the batch is heated in a hydrogen sulfide atmospherefor 3 to 8 hours at 900 to 1300 C. The optimum heat treatment; that is,the combination of heating time and heating temperature, for aparticular batch is determined empirically and is dependent in part onthe composition of the reaction product. The degree of heat treatment isgenerally lower as the content of cadmium, selenium, and tellurium isincreased at the expense of zinc and sulfur. A neutral atmosphere or avacuum may be used instead of a hydrogen sulfide atmosphere in both thecalcining and reacting steps. Some suitable gas atmospheres are: argon,neon, nitrogen, ammonia, and mixtures thereof. After the heating iscompleted, the reaction product is cooled to room temperature and isready for use as a phosphor. T 0 improve homogeneity, the reactionproduct may be ground and refired one or more times. If a flux has beenused, any excess flux may be removed by leaching.

' When excited by 3660 angstrom ultraviolet light, most phosphorsdescribed in the examples below luminesce both at room temperature andat liquid nitrogen temperature (77 K.). The emission is principally innarrow bands, many of which appear to be associated with thecharacteristic 4f4f transitions of the particular rare earth activatorincorporated in the host material. In addition to these narrow bands,there is, in many samples a broad band, either separate or lying beneaththe narrow bands and dominated by the narrow bands.

Phosphor Examples 8-11 are electroluminescent and are thus especiallysuited for electric field excitation.

10 Example 1 Mix zinc sulfide with 1.0 mol percent ErCl Calcine themixture as described above. Then, heat the calcined mixture at about1150 C. for about 1 hour in a hydrogen sulfide atmosphere free ofoxygen, and then cool the reaction product to room temperature. Theproduct is a phosphor having the approximate molar composition ZnS:0.01Er which exhibits a luminescent emission peaked at about 5350 angstroms.

Example 2 Mix zinc sulfide with 0.1 mol percent DyF and calcine themixture as described above. Heat the calcined mixture at about 1150 C.for about 1 hour in a hydrogen sulfide atmosphere which is free ofoxygen, and then cool the reaction product. The product is a phosphorhaving the molar composition ZnS:0.001 Dy and exhibits a luminescencewhich peaks at about 5750 angstroms.

Example 3 Mix and calcine ZnS with 0.1 mol percent TbF as in Example 2.Then heat the calcined mixture for about 3 hours,at about 1150 C. in anoxygen-free hydrogen sulfide atmosphere. The product is a phosphorhaving the molar composition ZnS:0.001 Tb and exhibits a luminescencewhich peaks at about 5500 angstroms.

Example 4 Mix and calcine ZnS with 0.1 mol percent HoF as in Example 2.Then heat the calcined mixture for about 3 hours at about 1150 C. in anoxygen-free hydrogen sulfide atmosphere. The product is a phosphorhaving the molar composition ZnS:0.001 H03+ and exhibits a luminescencewhich peaks at about 4975 angstroms.

Example 5 Mix zinc sulfide with 0.1 mol percent TmF and then calcine themixture as described above. Heat the calcined mixture at about 1150 C.for about 1 hour in a hydrogen sulfide atmosphere free of oxygen, andthen cool the reaction product. The reaction product is a phosphorhaving the approximate molar composition ZnS:0.001 Tm and which has aluminescent emission band centered at about 4773 angstroms with a bandwidth of about 50 angstroms. Sharp components of this band may be moreor less noticeable. No color shift has been observed with changes inexcitation level.

Example 6 Example 7 Mix zinc sulfide with 0.01 mol percent of thuliumchloride and 0.01 mol percent of lithium chloride and calcine at 120 C.Heat the calcined mixture in a hydrogen sulfide atmosphere for one-halfhour at 800 C. and then for one-half hour at 1200 C. The resultantproduct is a phosphor having an emission band which peaks at about 4773angstroms and which is about 70 angstroms wide.

Example 8 Mix grams of pure zinc sulfide with 0.1 gram copper as cuprouschloride and 0.1 gram erbium, as the chloride, and then calcine themixture as described above. Heat the calcined mixture at about 1150 C.for about 3 hours in an atmosphere of hydrogen sulfide which is free ofoxygen, and then cool the reaction product to room temperature. Thereaction product has the approximate molar composition ZnS:0.001 Cu+:O.001 Er and exhibits a luminescept emission about 5250 angstromsunder excitation with a 10,000 cycle electric field.

Example -9 Mix 100 grams pure ZnS with 0.1 gram copper as cuprouschloride and 0.1 gram erbium, as the fluoride, and then calcine themixture. Mix the calcined mixture with 20 weight percent NaCl. Heat theresultant mixture at about 1000 C. for about 1 hour in an atmosphere ofhydrogen sulfide which is free of oxygen, and then cool the reactionproduct to room temperature. The reaction product has the approximatemolar composition ZnS:0.001 Cu +:0.001 Er and exhibits a luminescentemission in narrow bands which peak at about 300 angstroms when excitedwith a 10,000 cycle electric field.

Example 10 Mix and calcine ZnS with 0.1 mol percent TbF and 0.1 molpercent CuCl as in Example 9. Then heat the calcined mixture for about 3hours at about 1150 C. in an oxygen-free hydrogen sulfide atmosphere.The product is a phosphor having the approximate molar compositionZnS:0.001 Cu +:0.00l Tb and exhibits an electroluminescence which peaksat about 5500 angstroms.

Example 11 Mix and calcine ZnS with 0.1 mol percent H01 and 0.1 molpercent CuCl as in Example 10. Then heat the calcined mixture for about3 hours at about 1150 C. in an oxygen-free hydrogen sulfide atmosphere.The product is a phosphor having the approximate molar compositionZnS:0.00l Cu +:0.00l Ho and exhibits an electroluminescence which peaksat about 4975 angstroms.

What is claimed is:

1. The combination of:

(a) an image device comprising a phosphor screen and means for excitingsaid screen to luminescence, said screen including a phosphor having anemission band whose width is not greater than one-fiftieth the visiblespectrum and having a peak emission intensity which is at least sixtimes the peak emission intensity of the standard P1 phosphor, and

(b) optical filter means through which an observer may view said screen,said filter means being disposed between said observer and substantiallyall the ambient light and having a transmission band whose width is notsubstantially greater than one-fortieth the visible spectrum and whichtransmission band is substantially centered with respect to saidemission band.

2. The combination of:

(a) an image device comprising a phosphor screen and means for excitingsaid screen to luminescence, said screen including a phosphor having anemission band whose width is not greater than 75 angstroms, and having apeak emission intensity which is at least six times the peak emissionintensity of the standard P1 phosphor, and

(b) optical filter means through which an observer may view said screen,said filter means comprising spectacles adapted to be worn by saidobserver and including lenses each of which has a transmission bandwhose width is not substantially greater than 100 angstroms and which iscentered with respect to said emission band.

3. The combination of:

(a) an image device comprising a phosphor screen and means for excitingsaid screen to luminesence, said screen including a blue-emittingnarrow-band phosphor and a yellow-emitting narrow-band phosphor, theemission band of each of said phosphors having a width not greater than'75 angstroms and being spaced from the emission band of the other ofsaid phosphors, and

(b) spectacle means through which said screen may be viewed, saidspectacle means comprising an optical filter having a transmission bandsubstantially matched to the emission band of one of said phosphors.

4. The combination of:

(a) an image device comprising: a mosaic phosphor screen includingseparate discrete deposits of a first phosphor and separate discretedeposits of a second phophor, and means for selectively exciting saidscreen to produce an emission of a desired color therefrom, each of saidfirst and second phosphors having an emission band which is not greaterthan 75 angstroms and which is spaced apart from'the emission band ofthe other of said phosphors, each of said first and second phosphorshaving a peak emission intensity which is at least six times the peakemission intensity of the standard P1 phosphor, and

(b) optical filter means having a first transmission band which issubstantially matched to the emission band of said first phosphor and asecond transmission band which is substantially matched to the emissionband of said second phosphor, each of said transmission bands having awidth not greater than angstroms.

5. The combination of:

(a) an image device comprising a phosphor screen and means for excitingsaid screen to luminescence, said screen including a first phosphor anda second phosphor, said second phosphor having an emission band whosewidth is not greater than one-tenth the emission band width of saidfirst phosphor and which lies outside the emission band of said firstphosphor, said second phosphor having a peak emission intensity which isat least four times the peak emission intensity of said first phosphor,said phosphors being mixed together in such proportions that theluminescent emission of said screen appears white to the unaided eye,and

(b) optical filter means adapted to be disposed between an observer andthe ambient light and through which said screen may be viewed, saidfilter means having a transmission band which is not substantiallygreater than 100 angstroms and which is centered with respect to theemission band of said second phosphor.

6. The combination of:

(a) an image device comprising a mosaic phosphor screen includingseparate discrete deposits of a first phosphor, a second phosphor, and athird phosphor, and means for exciting said screen to luminescence, eachof said phosphors having a peak emission intensity which is at least sixtimes the peak emission intensity of the standard P1 phosphor, theemission bands of said phosphors being spaced apart from each other, and

(b) optical filter means spaced from said image device through whichsaid screen may be viewed, said filter means having three spaced-apartnarrow transmission bands each of which is substantially matched to theemission band of a diiferent one of the phosphors of said screen.

7. In a system wherein three observers may simultaneously view aphosphor screen on which three different color images are simultaneouslydisplayed, the combination of:

(a) an image device comprising a mosaic phosphor screen including afirst array of discrete deposits of a first phosphor, a second array ofdiscrete deposits of a second phosphor, and a third array of discretedeposits of a third phosphor, and means 13 for selectively exciting saidthree arrays to produce three separate difierent color images, each ofsaid phosphors having a peak emission intensity which is at least sixtimes the peak emission intensity of the standard P1 phosphor.

(b) first optical filter means adapted to be worn by a first observerand having a transmission band which is substantially centered withrespect to the peak emission of said first phosphor,

-(c) second optical filter means adapted to be Worn by a second observerand having a transmission band which is substantially centered withrespect to the peak emission of said second phosphor, and

((1) third optical filter means adapted to be worn by a third observerand having a transmission band which is substantially centered withrespect to the peak emission of said third phosphor,

(e) the three transmission bands of said first, second, and thirdoptical filter means being spaced apart from each other so as todiscriminate between the luminescence of said three different phosphors.

8. The combination of:

(a) an image device comprising a mosaic phosphor screen includingseparate discrete deposits of first, second, and third phosphors, andmeans for selectively exciting said phosphors to produce emission of aselected color, each of said phosphors having a peak emission intensitywhich is at least six times the peak emission intensity of the standardP1 phosphor and an emission band whose width is not greater than 100angstroms, the emission bands of said phosphors being spaced-apart fromeach other.

(b) first optical =filter means adapted to be worn by a first observerand having a transmission band whose width is not greater than 100angstroms and which is substantially centered with respect to theemission band of said first phosphor.

(c) second optical filter means adapted to be worn by a second observerand having a transmission band Whose width is not greater than 100angstroms and which is substantially centered with respect to theemission band of said second phosphor,

(d) third optical filter means adapted to be worn by a third observerand having a transmission band whose width is not greater than 100angstroms and which is substantially centered with respect to theemission band of said third phosphor, and

(e) the three transmission bands of said first, second, and thirdoptical filter means being spaced apart from each other so as todiscriminate between the luminescence of said three phosphors.

9. The combination of:

(a) an image device comprising a phosphor screen and means for excitingsaid screen to luminescence, said screen including a blue-emittingnarrow band phosphor and a yellow-emitting narrow band phosphor, theemission bands of said phosphors being not greater than angstroms eachand being spaced apart from each other, and

(b) spectacle filter means adapted to be worn by an observer, saidspectacles having a transmission band substantially matched to theemission band of one of said phosphors, each of said transmission bandhaving a width not greater than angstroms.

References Cited UNITED STATES PATENTS 2,307,188 1/ 1943 Bedford 178-6.52,644,854 7/1953 Sziklai 1787.86 3,250,722 5/1966 Borchardt 252301.4

ROBERT L. GRIFFIN, Primary Examiner.

J. A. ORSINO, JR., Assistant Examiner.

US. Cl. X.R.

533 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,454,715 Dated 8, 1969 Inventor) Simon Larach, Ross E. Shrader, PerryN. Yocom It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 8, line 14 "monchrome" should. be monochrome- Column 8, line 44"b O l to l. 0 mol" should be b 0 O to l. 0 mol- Column 9 line 15 after"intimately" insert -mixed- Column 10 line 57 change "4700" to 47S5Column 11 line 5 "luminescept" should be luminescent-- Column 11 line 66cancel "substantially" Column 11 line 67 after "is" insertsubstantial1y- Column 12 line 41 after "appears" insert substantially-Column 12 line 43 cancel "adapted to be" Column 12, lines 46 cancel"substantially" and 47 Column 12 line 47 after "is" insertsubstantially- Column 14, line 24 cancel "each of" SIGNED AND SEALED OCT21 1969 (SEAL) L. Arrest:

idwartl M. Fletcher, Ix. 2 R. 6a m ttcstmg Officer fimfilflloga or n".

